Image blur caused by camera shake is a common problem in photography. The problem is especially acute when a lens of relatively long focal length is used, because the effects of camera motion are magnified in proportion to the lens focal length. Many cameras, including models designed for casual “point and shoot” photographers, are available with zoom lenses that provide quite long focal lengths. Especially at the longer focal length settings, camera shake may become a limiting factor in a photographer's ability to take an unblurred photograph, unless corrective measures are taken.
Some simple approaches to reducing blur resulting from camera shake include placing the camera on a tripod, and using a faster shutter speed. However, a tripod may not be readily available or convenient in a particular photographic situation. Using a faster shutter speed is not always feasible, especially in situations with dim lighting. Shutter speed may be increased if a larger lens aperture is used, but larger-aperture lenses are bulky and expensive and not always available. In addition, the photographer may wish to use a smaller lens aperture to achieve other photographic effects such as large depth of field.
Various devices and techniques have been proposed to help address the problem of image blur due to camera shake. For example, Murakoshi (U.S. Pat. No. 4,448,510) uses an accelerometer to detect camera shake, and provides an indication to the user of the camera if the acceleration exceeds a threshold level. The photographer can then make appropriate adjustments.
Satoh (U.S. Pat. No. 6,101,332) also senses camera shake, and combines the shake information with other camera parameters to estimate how much image blur might result. A set of light emitting diodes communicates the estimate to the photographer, who can then make adjustments.
Another approach has been to automate the camera operation, and let the camera choose settings that will minimize blur. For example, Bolle et al. (U.S. Pat. No. 6,301,440) applies a variety of image analysis techniques in an attempt to improve several aspects of photographs.
Some cameras or lenses are equipped with image stabilization mechanisms that sense the motion of the camera and move optical elements in such a way as to compensate for the camera shake. See for example Otani et al. (U.S. Pat. No. 5,774,266) and Hamada et al. (U.S. Pat. No. 5,943,512).
In a digital camera, the photosensitive element is an electronic array light sensor onto which a scene image is projected by the camera's lens. Some recent digital cameras compensate for camera shake by moving the sensor in relation to the lens during the exposure in response to camera motions so that the sensor approximately follows the scene image projected onto it, thus reducing blur.
Some digital cameras, especially video cameras, rather than move the electronic array light sensor, dynamically select a subregion of the sensor from which to take a photograph. The subregion selection is made in response to camera motion so that camera shake is compensated.
When an active stabilization technique is used, whether motion of an optical element, motion of an electronic array light sensor, or dynamic sensor region selection, the designer of the camera makes a compromise between compensating for camera motion that is assumed to be unintentional camera shake, and allowing for camera motion that is assumed to be intentional composition or framing of a photograph. Typically, high-frequency motion, for example oscillation faster than about 1 Hz, is assumed to be unintentional, while constant or low-frequency motion is assumed to be purposeful. For example, if a photographer in framing a photograph moves the camera slowly from one composition to another, the camera allows its field of view to track to the new composition. The camera continues to compensate for high-frequency oscillations, but does not completely compensate for the relatively low-frequency composition or aiming motions so that photographic composition can still be accomplished.
Due to the nature of motion control systems, there is a delay or settling time while the image stabilization system tracks to the new composition.